Problem solved as follows, might be interesting for someone having same issue

It is indeed in /etc/crontab that the problem occured, though we couldn't find out why

Kevin (Thanks man) from support fiddled around and basically deleted the lines in that file and retyped it.... and gone is the problem... as said something in the line was bad but what ?? I looked afterwards closely on the other server and compaired the lines from the now working crontab and the 'corrupt' one and couldn't find anything different, even counted spaces etc.....

Anyway, I copied the content, rm crontab, touch crontab and pasted the content back in and .... no errors anymore...

Well a few others pop up now since that is running back normal but... that's maybe for another topic